JPS6235313B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image quality improvement device for sharpening the contour of a video signal in a television receiver to improve the sharpness of a reproduced image.

There is an upper limit to the transmission band of the video signal processing system in a television receiver, and the video signal reproduced from the received television signal, especially the high-frequency component of the luminance signal, is greatly attenuated and the horizontal resolution of the reproduced image is reduced. becomes lower. As a method of compensating for such rounding of the waveform of a video signal, a compensation circuit based on a second-order differential method has been conventionally used. FIG. 1 shows a waveform diagram illustrating the outline of this operation. By differentiating the signal whose high-frequency components have been attenuated by the signal processing system of the television receiver [a in Figure 1] twice, a signal with waveform b is obtained, and when this signal b is subtracted from the original signal a, the signal is c is obtained. Here, when signal c is compared with signal a, the rise and fall portions are steeper, indicating that the image quality can be improved. However, with this method, before and after the rising and falling parts of the video signal,
This may result in wide preshoots or overshoots, which may improve the apparent resolution, but often overemphasizes the contours and results in an unnatural image.

SUMMARY OF THE INVENTION An object of the present invention is to provide an apparatus that eliminates the above-mentioned drawbacks of the prior art, improves the rise and fall characteristics of a video signal, and improves image quality.

To achieve this objective, the present invention detects the changing portion of a signal and uses the detected signal to
It switches between three signals with different delay times to obtain a signal with steep rises and falls.

Examples of the present invention will be described below. Second
The figure is a block diagram of one embodiment of the present invention, and FIG. 3 is an operational waveform diagram thereof. 1 is a delay line as a signal generating means, which delays the input signal d by a predetermined time;
first and second delayed video signals e having a first delay time and a longer second delay time;
make f. 3 and 5 are differentiating circuits that receive signals e and e, respectively.
Differentiate h to create signals g and i. 4 is a double-wave rectifier circuit that rectifies the signal g from the differentiator circuit 3 and converts it into a signal h.
make. 6 is an inverting amplifier circuit which inverts the signal i to generate the signal j. Reference numeral 2 designates a changeover switch as a selection means for selecting a signal, and is controlled by signals i and j.

Next, the operation of this embodiment will be explained. input
The signal d applied to in is the terminal of changeover switch 2.
S ₃ and fed to delay line 1. Signals e and f each delayed for a predetermined time by delay line 1
is applied to the terminals S ₂ and S ₁ of the changeover switch 2. The changeover switch 2 is controlled by a control means that generates a signal i obtained by processing the signal e in differentiating circuits 3 and 5 and a double-wave rectifier circuit 4, and a signal j obtained by inverting the signal i.
As will be described later, signals from each terminal S ₁ , S ₂ , and S ₃ are selectively output according to the combination of signals i and j. That is,
If the signals i and j are below the level indicated by the broken line, the changeover switch 2 is connected to the terminal _S2 and outputs the signal e. Moreover, if only the signal i is above the level indicated by the broken line, the changeover switch 2 is connected to the terminal S 1 and the signal f is connected to the terminal _S1 .
Output. Similarly, if only the signal j is above the level indicated by the broken line, the changeover switch 2 is connected to the terminal _S3 and outputs the signal d.

In other words, the signal f is selectively output during the first half of the period in which a transient change occurs in the signal e, the signal d is selectively output in the second half of the period, and the signal e is selectively output during the period in which the signal e does not undergo a transient change. , the signal e is selected and output.

In this way, the connection to each terminal S ₁ to _{S 3} of the changeover switch 2 is controlled according to the combination of signals i and j,
Any one of signals d, e, f with different delay times
By sequentially selecting and outputting the two, it is possible to obtain a video signal with steep rises and falls, as shown by the solid line in FIG. 3k. The reference level for determining the level of the signals i and j (the level indicated by the broken line in the figure) is determined by the transistors TR ₇ and
This corresponds to each base potential of TR ₁₀ and TR ₁₃ , and as this potential becomes higher, the degree of compensation decreases, and conversely, if it is too low, the contour portion becomes too emphasized. Under normal conditions, this reference level is 2
It is preferable to set it near the average level of the twice differentiated waveforms i and j. In addition, what is shown by the broken line in FIG. 3k is the waveform e corresponding to the input signal, and the degree of improvement can be clearly seen by comparing the two.

An example of a circuit embodying the embodiment of the present invention shown in FIG. 2 is shown in FIG. A delay line with a delay time of about 0.03 to 0.05 μs is used as delay line 1, and switch 2 is connected to transistors TR ₆ , TR ₇ , TR ₈ and
It consists of three differential amplifiers consisting of TR ₁₀ , TR ₁₁ and TR ₁₃ , TR ₁₄ , and the differentiating circuits 3 and 5 each have a capacitor C ₁ and a resistor R ₁ , and a capacitor C ₂ and a resistor.
It consists of a CR type consisting of _R2 . The double-wave rectifier circuit 4 rectifies the output of a differential amplifier consisting of transistors TR ₁ and TR ₂ using diodes D ₁ and D ₂ . The inverting amplifier circuit 6 uses a commonly used inverting amplifier circuit. The signal d applied to input in is applied to delay line 1 and to the base of transistor _TR15 . Of the signals e and f delayed by a predetermined time, the signal e is applied to the capacitor _C1 of the differentiating circuit 3 and the base of the transistor _TR9 , and the signal f is applied to the base of the transistor _TR12 . The signal e applied to the differentiator circuit 3 is a capacitor
It is differentiated by C ₁ and resistor R ₁ and applied to the base of transistor TR ₁ . At the connection point between the diodes D ₁ and D ₂ , a signal h is obtained by folding back the negative direction signal of the signal g. This signal h is a capacitor
The signal i is differentiated by C ₂ and the resistor R ₂ and is applied to the bases of the transistors TR ₆ and TR ₁₁ of the changeover switch 2 and the base of the transistor TR ₄ of the inverting circuit 6. The signal j passed through the inverting circuit 6 is applied to the bases of the transistors TR ₈ and TR ₁₄ of the changeover switch 2. Further, the bases of the transistors TR ₇ , TR ₁₀ and TR ₁₃ of the changeover switch 2 are resistively divided from +B and biased. As previously mentioned, this bias determines the reference levels shown in Figures i, j. Transistor of switch 2
The collectors of TR ₆ , TR ₈ , TR ₁₀ , TR ₁₃ are directly +B
are connected to transistors TR ₇ , TR ₁₁ ,
The collector of TR ₁₄ is connected to +B via a common resistor R ₃ .

Therefore, if we consider the reference level shown by the broken line as the bias voltage of the changeover switch 2 along with the signals i and j in FIG. 3, at time t ₁ →t ₂ in FIG. The transistor TR ₇ conducts and outputs a signal e to the resistor R ₃ and thus to the output terminal OUT. At time t ₂ →t ₃ , signal i becomes higher than the bias voltage, transistors TR ₆ and TR ₁₁ conduct, and output signal f. At time t ₃ →t ₄ , signal j becomes higher than the bias voltage, transistors TR ₈ and TR ₁₄ conduct, and output signal d. Similarly, from time _t5 onward, one signal is selectively output from signals d, e, and f, so
The signals appearing at the output from time t ₁ to _{t 9} are as follows: t ₁ →t ₂ ; e t ₂ →t ₃ ; f t ₃ →t ₄ ;d t ₄ →t ₆ ;e t ₆ →t ₇ ;f t ₇ →t ₈ ;d t ₈ →t ₉ ;e.

This is illustrated as signal k in FIG. 3. As you can see, the rise and fall are steep.

As described above, according to the present invention, it is possible to sharply compensate for the contour portion of the corrected signal waveform without preshooting, overshooting, etc., and it is possible to obtain a natural image.

In the above description, it has been explained that the differentiating circuit 3 is supplied with a signal having the same delay time as the signal e applied to the terminal _S2 of the changeover switch. Of course, this makes it possible to improve the image quality without causing any practical problems, but to be very precise, the signal processing in the differentiating circuits 3, 5, the double-wave rectifying circuit 4, the inverting circuit 6, etc. results in twice differentiated output. Signals i and j will have some phase lag compared to signal e, resulting in discontinuities and distortions in the composite output waveform k. In order to avoid this, the signal supplied to the differentiating circuit 3 should be designed in advance so that it has a shorter delay time corresponding to the phase delay than the signal directly applied to the terminal _S2 of the changeover switch. Just adjust it.

Specifically, for example, if a second output intermediate tap is provided between the first delayed video signal output intermediate tap and the input in the delay line 1 in FIG. 2, and its output is supplied to the differentiating circuit 3, good. Therefore, if the intermediate tap can be brought close enough to the input, the input signal itself can be supplied to the differentiating circuit 3.

[Brief explanation of the drawing]

Fig. 1 is a waveform diagram for explaining the image quality improvement mechanism using the conventional second-order differential method, Fig. 2 is a block diagram showing an embodiment of the present invention, Fig. 3 is a waveform diagram for explaining its operation, and Fig. 4. is an example of a circuit embodying the present invention. 1... Delay line, 2... Selector switch, 3, 5... Differential circuit, 4... Double wave rectifier circuit, 6... Inverting circuit.

Claims (1)

[Claims] 1. Generating a first delayed video signal having a first time delay from the input video signal, and a second delayed video signal having a second time delay from the first delayed video signal. a signal generating means; a selection means for selecting one of the input video signal and the first and second delayed video signals; , selects the second delayed video signal and the input video signal in the second half of the period, and selects the first delayed video signal during a period in which no transient change occurs in the first delayed video signal. An image quality improvement device comprising: control means for controlling the selection means. 2. The image quality improvement device according to claim 1, wherein the first and second time delays are chosen to be equal. 3 The control means includes: a first differentiating circuit that differentiates one of the input and the first delayed video signal; a rectifying circuit that double-wave rectifies the output of the first differentiating circuit; and a second differentiating circuit that differentiates the output of the rectifying circuit. The image quality improving device according to claim 1, comprising: a circuit; and an inverting circuit for inverting the output of the second differentiating circuit.